Hydrocarbon streams are refined through various unit operations to produce various types of fuel, industrial raw materials that are employed in production of other compounds or products, and petroleum-based products. Production of gasoline is a particularly important industrial process involving refining of hydrocarbons through various unit operations, including isomerization and catalytic reforming. Reforming of hydrocarbons is useful to convert paraffins to aromatic compounds in the presence of noble metal catalysts. Aromatic compounds provide high octane value and, thus, are desirable components in gasoline. Isomerization is effective to convert linear hydrocarbons into branched hydrocarbons, which have a higher octane value than linear compounds but a lower octane value than aromatic compounds. Isomerized streams (or isomerate) are substantially free of aromatic compounds, whereas reformate streams (or reformate) generally include high quantities of aromatic compounds (e.g., at least 50 wt %).
During refining, a hydrocarbon stream is generally separated into various streams based on the number of carbon atoms of compounds within each stream. Hydrocarbons having 7 or more carbon atoms are generally subject to reforming because reforming generally results in higher octane value than isomerization of these hydrocarbons. Hydrocarbons having 5 or 6 carbon atoms are generally subjected to an isomerization process which has significant hydrogen requirements.
Hydrogen is an expensive commodity. The efficient use of hydrogen is very important to the economics of an isomerization process. In current designs of isomerization units, there is a significant amount of hydrogen that is currently not being recovered, such as the hydrogen that ends up in scrubber off-gas.
Accordingly, it is desirable to provide apparatuses and processes to economically recover hydrogen and to reduce the amount of makeup hydrogen that would be required in a C5/C6 isomerization unit, thus reducing the operating cost associated with producing the hydrogen. Further, it is desirable for increased recovery of C3-C4 hydrocarbons such as liquefied petroleum gas (LPG) from the scrubber off-gas. Furthermore, other desirable features and characteristics of the present subject matter will become apparent from the subsequent detailed description of the subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the subject matter.